We propose to characterize cultures of human and bovine aortic endothelial cells and canine arterial endothelial cells in terms of: (1) growth characteristics (human, bovine and canine); (2) morphology and ultrastructure (human, bovine and canine); (3) certain biochemical properties such as the type and ultrastructural localization of collagen (bovine) and contractile protein (bovine). We also propose to utilize the cultured bovine endothelial cells, and ultimately, the human endothelial cells, as a model system to study the nature and mechanism of platelet-endothelial interaction and the factors (rheological, mechanical and biochemical) which may enhance or prevent this interaction. Finally, we propose to examine the possibility of endothelializing a dacron prosthesis in vitro prior to implantation in a dog. The endothelial cells will be obtained by arterial biopsy, the cells will be grown on the prosthesis in culture in the presence of H3-thymidine, and the prosthesis implanted in the same animal. The thymidine label should allow the determination of the percentage of original cells still remaining on the prosthesis at subsequent time periods.